A power fault in the city about 4.55am (AEST) on Tuesday was caused by an overhead contact cable which broke at North Melbourne station and triggered a short circuit, affecting the viaduct between Southern Cross and Flinders Street stations.

The outage plunged part of the Southern Cross station into darkness and stranded commuters travelling in and out of the major terminus.

V/Line passengers travelling to and from regional Victoria and interstate were also hit.

Mr Pakula said Metro Trains had received more maintenance funding than any other operator but conceded more work was required.

"There are kilometres and kilometres of overhead cable that have already been replaced but there are obviously a lot more areas of the network that are going to continue to need overhead wire replacement," he told reporters.

"This particular piece of cable that snapped is one that they haven't done yet."

He said the widespread chaos on Tuesday was regrettable and said both the government and Metro all needed to take responsibility for the incident.